Field of the Invention
This invention relates to designs and methods for increasing the natural frequency of fuel cell stacks and particularly for increasing the natural frequency to prevent damage from resonance in automotive fuel cell stacks.
Description of the Related Art
Fuel cells such as solid polymer electrolyte membrane fuel cells electrochemically convert reactants, namely fuel (such as hydrogen) and oxidant (such as oxygen or air), to generate electric power. Solid polymer electrolyte fuel cells generally employ a proton conducting, solid polymer membrane electrolyte between cathode and anode electrodes. A structure comprising a solid polymer membrane electrolyte sandwiched between these two electrodes is known as a membrane electrode assembly (MEA). In a typical fuel cell, flow field plates comprising numerous fluid distribution channels for the reactants are provided on either side of a MEA to distribute fuel and oxidant to the respective electrodes and to remove by-products of the electrochemical reactions taking place within the fuel cell. Water is the primary by-product in a cell operating on hydrogen and air reactants. Because the output voltage of a single cell is of order of 1V, a plurality of cells is usually stacked together in series for commercial applications in order to provide a higher output voltage. Fuel cell stacks can be further connected in arrays of interconnected stacks in series and/or parallel for use in automotive applications and the like.
Fuel cell stacks thus typically comprise numerous, thin, fragile components. For various technical reasons relating to cell function, the dimensions of individual cells in a solid polymer electrolyte fuel cell stack can have high aspect ratios (e.g. length>>width>>>thickness). And in automotive or other vehicle applications, for various reasons relating to vehicle function and design, the desired dimensions of the fuel cell stacks can also have relatively high aspect ratios. In particular, in stacks with numerous cells, the stack height may be much greater than the stack/cell width.
As disclosed in U.S. Pat. No. 5,789,091, for simplicity and in order to minimize weight and volume, stacks may be secured in a compressed, assembled state using one or more compression bands which circumscribe end plate assemblies and interposed fuel cells of the stack. One or more resilient members are preferably employed which cooperate with each compression band to urge the first end plate assembly toward the second end plate assembly. And compressive force is thus applied to promote sealing and electrical contact between the layers forming the fuel cell stack. Strips of electrically insulating material may be interposed between the compression bands and the edges of the fuel cells.
In vehicle applications, the on-board fuel cell stacks are subject to mechanical vibrations when the vehicle is in motion. And like the other components on-board, if the frequency of these vibrations is close to the natural frequency of the fuel cell stack, there is the possibility that the stack can resonate and be damaged as a result. This issue is disclosed in WO2012086344 and a design is proposed for increasing the resonant frequency of the stack without increasing the parts count. Here, a pair of reinforcing plates are connected to the end plates of the stack and cover outer peripheral faces of the laminate of fuel cells.
As development of commercial fuel cell stacks progresses, issues relating to vibration can be encountered more often. This is particularly so for motion induced vibration in vehicle applications. There will therefore be a corresponding need to resolve these issues in a simple manner with minimal increase in weight, volume, and parts count. This invention addresses this need and provides further related advantages.